A Russian biathlete became the first competitor at these Olympics to fail a drugs test and has been stripped of her silver medal. Olga Pyleva tested positive after finishing second in the 15km biathlon on Monday for carphedon, a stimulant developed in Russia and which is claimed to increase physical endurance and resistance to the cold.

The disqualification of Pyleva, the gold medalist in Salt Lake City four years ago, means Germany's Martina Glagow wins silver and the Russian Albina Akhatova bronze.

"Doping cases are things that happen in Olympic Games," said the IOC president Jacques Rogge. "We have to tackle that and we are doing that with great energy." Pyleva is not only set to receive a two-year ban by the International Biathlon Union but could face a prison sentence of between three months and two years under Italy's strict anti-doping laws, although that is likely to be waived.

Dr Nikolai Durmanov, head of the Russian anti-doping committee, said the doctor who treated her in the Siberian city of Krasnoyarsk for an ankle injury in January gave her an over-the-counter medication that did not list carphedon among its ingredients.

"This was 100% the physician's mistake," he said. "The main point of our concern is our athletes, because she is innocent and she is in a catastrophe. Her brilliant career has been finished in such a dramatic way without her being guilty.

"The typical Russian way of doing things is immediately find somebody to blame. This case is much more complicated. I can blame myself. We have brought a lot of extra new equipment in our lab, we have published a lot of books, leaflets, brochures for our athletes, for medicine workers, but finally it didn't work. So it's my responsibility too."

Carphedon is related to bromantan, a substance which several Russians tested positive for at the 1996 Olympics in Atlanta but escaped punishment because at the time it was not listed by the International Olympic Committee on its banned list.

Britain's men's and women's curling teams continued their impressive early form as they both recorded wins yesterday. David Murdoch's rink are top of the rankings after beating Germany 7-6, their fourth victory in five matches. Rhona Martin's women share the lead with Sweden, Switzerland and Norway following their 10-4 win against Russia, as they aim to defend the title Great Britain won in 2002.

Estonia's Kristina Smigun became the first double medallist of the Winter Games with victory in the 10km classical cross country, following her 15km pursuit gold on Sunday.